The work vehicles such as the wheel loaders have been operated for executing works with various types of attachments (working units) such as a bucket or a fork. A suitable one of the attachments is herein selected in accordance with work content and is attached to the tips of booms rotatably mounted to the front part of the vehicle body.
For example, Patent Literature 1 describes a wheel loader embedded with a Z-bar link as a mechanism for driving the aforementioned working unit (e.g., a bucket and a fork). In the wheel loader, the Z-bar link can perform an action similar to that of a parallel link mechanism. In the present specification, the mechanism using the Z-bar link described in Patent Literature 1 and the parallel link mechanism will be hereinafter collectively referred to as “a parallel link motion mechanism”.
Specifically, the parallel link motion mechanism is configured to keep a fork attached as a working unit to the booms in a parallel position to the ground in elevating the booms from a position where the fork is disposed on the ground. Therefore, operators can operate the work vehicles (e.g., the wheel loaders) equipped with the fork for executing a variety of works (e.g., loading of baggage) without adjusting the tilt angle of the fork.